1. Field of the Invention
The present invention relates to a method and a device for measuring intensity of electromagnetic field which is formed by electromagnetic waves radiated outward from various kinds of electronic device.
2. Description of the Prior Art
As a method for measuring intensity of electromagnetic field due to electromagnetic waves radiated outward from electronic device as a measure to cope with EMI (ElectroMagnetic Interference), those such as described below have been specified. As an example, nominated is a method to implement measurement with a device-under test (DUT) being a piece of electronic device as an measurement object being disposed in an open space, and with a loop antenna or a dipole antenna being disposed at a distance of 3 m to 10 m from this DUT. Thus, in the case where an antenna has been disposed at an ample distance from the DUT, the loop antenna can measure only magnetic component of the far-remote radiation electromagnetic field, and the dipole antenna can measure only electric field component thereof. And one component of the far-remote radiation electromagnetic field being measured, the other can be calculated. In addition, a method for implementing measurement not in an open space but in a radio darkroom has also been specified.
On the other hand, there is also a case where the radiation source of an electromagnetic wave is specified. For example, this takes place in the case where it is specified that from which part on a circuit substrate the electromagnetic wave is being intensively radiated. In such a case, unlike the said measurement, the intensity of electromagnetic field is measured adjacent to the DUT. In general, a small loop antenna is made to approach the DUT and the magnetic field component is measured. That is, in this method, the magnetic field component of the electromagnetic field due to the DUT is measured by using the dielectric electromotive force due to magnetic coupling. In addition, based on the result of this measurement, current-voltage distribution in the DUT is obtained and the radiation source is specified.
Incidentally, a method utilizing the said open space or radio darkroom requires a vast disposing space and a large amount of device investment. Therefore, in recent years, as an assessment method on intensity of radiated electromagnetic waves, an assessment method utilizing a coaxial transmission line called TEM Cell (Transverse ElectroMagnetic Cell) attracts public attention. In this assessment method, assessment is implemented with a DUT being disposed between interior conductor and exterior conductor of the coaxial transmission line, and based on signals to be outputted from one end of interior conductor. This method is advantageous in its capability to implement assessment with a comparatively small device.
However, the method utilizing the TEM Cell has presented a problem that it cannot give correlation with measurement in an open space. That is, the problem is that since the DUT and the interior conductor come in close vicinity to each other in terms of distance, the output current from the TEM Cell can no longer ignore the current due to magnetic coupling and the-current due to electric coupling.
On the other hand, it is necessary to exclude influence by electric field component for the purpose of specifying in good accuracy the radiation source of the electromagnetic waves utilizing the said loop antenna. Therefore, shielded loop antenna in which a loop antenna has undergone shielding are often used. With this shielded loop antenna, which is hardly influenced by the electric field component, measurement only on the magnetic field component can be implemented comparatively highly accurately.
However, even with a shielded loop antenna, which will give rise to an electric field coupling between itself and the test sampling device in the section having not undergone shielding due to its configuration problems, it will be difficult to measure only magnetic field component accurately. In addition, configuration comprising shielded sections makes it difficult to implement miniaturization. That is, it was difficult to improve resolution capacity.